From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E807B35C185; Wed, 3 Dec 2025 16:36:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764779786; cv=none; b=shWomNP41GsDYQtf9/BsWEITqVMODaFXD7IN/9DQDPZYdgpfDv3nTmKtsRLhfQx1qORmlXLsONpMIVypEd9w3/JM6miVrTVroM938CO1p1XP2/pu9zkS+YR7dVfCRT+YZ2Y2KA0MOsABfSUxEdDJIFqh+4SxUXtNXJAHSpl9GAY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764779786; c=relaxed/simple; bh=pzy4ngyhsZnf+fTbptz6JI8FvOEtOCOc4U5Jj8p5iXM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=R4uIVW0cGVERbP6EujprhN5GaCE7vyhlI2vJVp47vKcd4DMqbfurNswLxzRaokXDpeEPYGXSGfTa+Pq1iI3Q9JvEQZKlpS0gWBRKBdocGK4TQU2AY0efjJBQzeFGKb5iiOVetBMtr/mjkn0IJG6jjOf3gaBZ/JKWZtgJi4Vcws8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=CVSEvP+X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="CVSEvP+X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4CDF9C4CEF5; Wed, 3 Dec 2025 16:36:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1764779785; bh=pzy4ngyhsZnf+fTbptz6JI8FvOEtOCOc4U5Jj8p5iXM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CVSEvP+XMxrvg2MC3vYT0n1hzt6kA+kkYd4RK/jpNaxYWk0ycMzjTsZ5urFL15cif owevNYhyWrAm/Ae2RoQGwasfgxeylQidhB/5Ot4cakGg2At9SJHBf0/i7d7w5+r50v t8g36vKXM28XQgIYSxgjybzhyCvcR+Jc/AoRGfm8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Quang Le , Kuniyuki Iwashima , Paolo Abeni , Sasha Levin Subject: [PATCH 6.1 361/568] af_unix: Initialise scc_index in unix_add_edge(). Date: Wed, 3 Dec 2025 16:26:03 +0100 Message-ID: <20251203152453.923836073@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251203152440.645416925@linuxfoundation.org> References: <20251203152440.645416925@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kuniyuki Iwashima [ Upstream commit 60e6489f8e3b086bd1130ad4450a2c112e863791 ] Quang Le reported that the AF_UNIX GC could garbage-collect a receive queue of an alive in-flight socket, with a nice repro. The repro consists of three stages. 1) 1-a. Create a single cyclic reference with many sockets 1-b. close() all sockets 1-c. Trigger GC 2) 2-a. Pass sk-A to an embryo sk-B 2-b. Pass sk-X to sk-X 2-c. Trigger GC 3) 3-a. accept() the embryo sk-B 3-b. Pass sk-B to sk-C 3-c. close() the in-flight sk-A 3-d. Trigger GC As of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices, and unix_walk_scc() groups them into two different SCCs: unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START) unix_sk(sk-X)->vertex->scc_index = 3 Once GC completes, unix_graph_grouped is set to true. Also, unix_graph_maybe_cyclic is set to true due to sk-X's cyclic self-reference, which makes close() trigger GC. At 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and links it to unix_unvisited_vertices. unix_update_graph() is called at 3-a. and 3-b., but neither unix_graph_grouped nor unix_graph_maybe_cyclic is changed because both sk-B's listener and sk-C are not in-flight. 3-c decrements sk-A's file refcnt to 1. Since unix_graph_grouped is true at 3-d, unix_walk_scc_fast() is finally called and iterates 3 sockets sk-A, sk-B, and sk-X: sk-A -> sk-B (-> sk-C) sk-X -> sk-X This is totally fine. All of them are not yet close()d and should be grouped into different SCCs. However, unix_vertex_dead() misjudges that sk-A and sk-B are in the same SCC and sk-A is dead. unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong! && sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree ^-- 1 in-flight count for sk-B -> sk-A is dead !? The problem is that unix_add_edge() does not initialise scc_index. Stage 1) is used for heap spraying, making a newly allocated vertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START) set by unix_walk_scc() at 1-c. Let's track the max SCC index from the previous unix_walk_scc() call and assign the max + 1 to a new vertex's scc_index. This way, we can continue to avoid Tarjan's algorithm while preventing misjudgments. Fixes: ad081928a8b0 ("af_unix: Avoid Tarjan's algorithm if unnecessary.") Reported-by: Quang Le Signed-off-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20251109025233.3659187-1-kuniyu@google.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/unix/garbage.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/net/unix/garbage.c b/net/unix/garbage.c index 0068e758be4dd..66fd606c43f45 100644 --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -136,6 +136,7 @@ enum unix_vertex_index { }; static unsigned long unix_vertex_unvisited_index = UNIX_VERTEX_INDEX_MARK1; +static unsigned long unix_vertex_max_scc_index = UNIX_VERTEX_INDEX_START; static void unix_add_edge(struct scm_fp_list *fpl, struct unix_edge *edge) { @@ -144,6 +145,7 @@ static void unix_add_edge(struct scm_fp_list *fpl, struct unix_edge *edge) if (!vertex) { vertex = list_first_entry(&fpl->vertices, typeof(*vertex), entry); vertex->index = unix_vertex_unvisited_index; + vertex->scc_index = ++unix_vertex_max_scc_index; vertex->out_degree = 0; INIT_LIST_HEAD(&vertex->edges); INIT_LIST_HEAD(&vertex->scc_entry); @@ -480,10 +482,15 @@ static void __unix_walk_scc(struct unix_vertex *vertex, unsigned long *last_inde scc_dead = unix_vertex_dead(v); } - if (scc_dead) + if (scc_dead) { unix_collect_skb(&scc, hitlist); - else if (!unix_graph_maybe_cyclic) - unix_graph_maybe_cyclic = unix_scc_cyclic(&scc); + } else { + if (unix_vertex_max_scc_index < vertex->scc_index) + unix_vertex_max_scc_index = vertex->scc_index; + + if (!unix_graph_maybe_cyclic) + unix_graph_maybe_cyclic = unix_scc_cyclic(&scc); + } list_del(&scc); } @@ -498,6 +505,7 @@ static void unix_walk_scc(struct sk_buff_head *hitlist) unsigned long last_index = UNIX_VERTEX_INDEX_START; unix_graph_maybe_cyclic = false; + unix_vertex_max_scc_index = UNIX_VERTEX_INDEX_START; /* Visit every vertex exactly once. * __unix_walk_scc() moves visited vertices to unix_visited_vertices. -- 2.51.0